Parallel rabbit holes if you like this stuff:

  - in Pokemon gen 1 you can wrap your stats back to zero by buffing them too much
  - In FF7 you can overflow the damage calculation to kill Ruby in one hit
  - Mario 64 has a mountain of usable glitches; "parallel universes" let you skip collisions at high speeds
  - GTA 3/VC/SA have crazy mission/wrong warp corruptions involving parallel game simulations
  - NES Mario can be corrupted to execute arbitrary code in TAS
  - OOT can be heap-corrupted so badly you can write a loader for an entire DLC via controller ("triforce%", my choice for most insane controller based hack of a game)